Being one of the essential elements in an automobile, an automobile interior rear-view mirror is a means used for observing the interior of an automobile. An automobile interior rear-view mirror is usually affixed to the glass of a front windshield via a mirror base of the rear-view mirror. Generally, OEMs require the front windshield having the mirror base of the rear-view mirror installed thereon before they leave for delivery and sell. It is accordingly significant to select a method adaptable to the process of a windshield to mount a rear-view mirror base onto the front windshield glass of an automobile.
Currently, the most commonly used method involves the use of a structural adhesive to fix the mirror base onto the front windshield glass.
The mirror base of an automobile interior rear-view mirror is a metallic part, whereas the front windshield glass is a non-metallic part, and thus they exhibit very different chemical structure and mechanical properties. Accordingly, a structural adhesive demand of high performance requirements, and specific requirements are as follows: (1) the structural adhesive is required to have good adhesion with the surfaces of the two materials to meet the requirement for stress, and exhibits a certain degree of flexibility and toughness after cure to achieve shock absorption during the running and braking process; (2) in the process of curing, the structural adhesive is not allowed to show any displacements in order to meet the requirement for the appearance of the front windshield glass; (3) the structural adhesive is required to have good cold-resistance and heat-resistance after cure; (4) the structural adhesive is required to have good processing properties to facilitate the production and processing process; (5) the curing process of the structural adhesive should be adapted with the processing process of the automobile front windshield glass. Currently, many types of adhesives are on the market, but they still cannot satisfy the above requirements for being the structural adhesive for use in the mirror base of an automobile interior rear-view mirror. Accordingly, production of a rapidly-cured structural adhesive specifically for use in the mirror base of an automobile interior rear-view mirror has great significance.
Currently, in the manufacturing industry of automobile glass, two types of adhesive are generally used in the mirror base of an automobile glass rear-view mirror: the polyurethane structural adhesive and the 3M specialized double-side adhesive tape. (1) the polyurethane adhesive: the adhesive is cured with the moisture in the atmosphere, and the polyurethane adhesive after cure exhibits good flexibility, adhesion, cold-resistance, heat-resistance, which properties comply with the requirements for the adhesive used in the mirror base of an automobile glass rear-view mirror. However, the curing time of the polyurethane adhesive is relatively long (3˜7 days), which renders the production efficiency low, and severely restricts the expansion of the capacity of the automobile glass manufacturing plant. In addition, the curing process of polyurethane adhesive is independent of the processing process of the front windshield glass, which complicates the preparation process of the front windshield glass. (2) the 3M specialized double-side adhesive tape: the curing process of the adhesive tape can be conducted simultaneous with the preparation process of the laminated windshield glass. The adhesive tape exhibits high strength after cure, and has a certain degree of toughness, which, however, is too expensive, and demands for harsh storage conditions (must be stored at a temperature of 5° C. or lower), which causes inconvenience to transport and the practical application.
A patent application (No. 201010005140.X) discloses a method for attaching the mirror base of a rear-view mirror to glass. In this patent, it is disclosed that a photo-curable glue is applied evenly onto the surface of the mirror base to be bonded, followed by subjecting it to ultraviolet irradiation to initiate the reaction of glue such that the mirror base of the rear-view mirror is bonded together with the glass, by which the curing process is made simplified, but the entire method become complicated for reason that one additional process is involved, which is unfavorable to the expansion of the capacity of the automobile glass manufacturing plant.
To sum up, it is hard for the existing adhesives to meet the requirements for being a structural adhesive used in an automobile interior rear-view mirror. Accordingly, it is important to provide a structural adhesive sheet specifically for use in the mirror base of the automobile interior rear-view mirror.